Fix 5335993, calculate correct size of lockscreen buttons

The buttons on the lockscreen were sized at startup time,
before the actual size of the keyboard's container (KeyboardView)
was known. Also, horizontal/vertical gaps were not taken into
account in calculating perecent sizes of the keys. This change
causes resize events (including the first one where the container
size is finally known) to recalculate the keys' sizes and positions
according to correct sizing of the container and the keyboard's gaps.

Change-Id: I5ba7a401226ed4b100e5739f3405388955d97997